Patent GB-632159-A (GB)
Title: Improvements in thermionic valve circuits
IPC: H03K4/16
Filed: 1946-06-06
Abstract: 632,159. Pulse and saw-tooth generating Circuits. WILLIAMS, F. C., and KILBURN, T. June 6, 1946, No. 17208. [Class 40 (vi)] In a generator in which a valve controls the withdrawal of charge from a storage device and negative feed-back is arranged to linearise the sweep, regenerative means including a unilaterally conducting device are arranged to operate during the intervals between sweeps to recharge the storage device. Sawtooth generating circuits. A negativegoing saw-tooth sweep is generated at the output 14, Fig. 2, of a "Miller" valve 7, the potential continuing to fall until the associated blocking oscillator valve 15 conducts to recharge rapidly capacitor 8. To reduce the effect of the negative swing of the grid of valve 15 being applied to the grid of valve 7, via capacitor 8, a capacitor 52 may be added. In a modification, Fig. 1 (not shown), valve 15 is replaced by a biassed diode, inductor being returned to the screen. grid of valve 7. Upon the diode conducting oscillation commences, the control and screen grid electrodes being effective. In a modification, Fig. 3, capacitor 8 discharges over resistor 10 to generate a negative going saw-tooth. To maintain a linear change in potential across the capacitor the waveform is fed to cathode follower 16, resistor 10 being returned to the junction of neon tube 17 and resistor 19. A further resistor may be included in the anode lead to give a push-pull output. Strobing pulse generating circuits. A pulse may be generated at the termination of the sweep, Fig. 4, by connecting a transformer 11, 12 to the screen and control grids, an artificial line 22, 23 being connected to the remote end of winding 12. The saw-tooth is applied to a circuit which generates the transmitter pulse of a radar set when a predetermined potential is reached. Variation of this potential shifts the strobe pulse relative to the transmitter pulse. During the sweep, the feed-back transformer is ineffective due to the heavy negative feed-back over capacitor 8. At the termination of the sweep, the negative feed-back is reduced, the grid potential rises causing the screen current to increase, thus driving the grid into heavy currents. A negative pulse is fed down the line 22, 23 and after reflection without change of sign cuts the valve off at the grid. The charging time of capacitor 8 and resistor 9 is made shorter than that of resistor 10 and the cathode-grid capacity so that when the valve commences to conduct the linear fall of anode potential occurs. The pulse may be taken from a third winding 21. In a further modification, Fig. 5, giving a large ratio of recurrence period to sweep, a potential divider 35, 37 is connected with a capacitor 36 and diode 38, the time constant of components 35, 36 being long compared with the sweep duration and short compared with the repetition period. Line 14 would thus fall below earth potential but due to diode 38 conducting the saw-tooth output is terminated when earth is reached, negative feed-back ceasing so that the blocking oscillation occurs, a negative pulse travelling down line 22, 23. The recurrence period is determined by the time constant 25, 27, the suppressor grid being driven negative by the pulse resulting from the blocking oscillation, thus cutting off anode current and allowing capacitor 8 to charge. The anode sweep recommences when capacitor 25 has discharged sufficiently for anode current to flow. Resistor 29 and capacitor 30 ensure that the rising screen current throughout the sweep does not cause a sufficient change in screen and suppressor grid potential to effect the linearity of the sweep. A biassed diode 33 is connected to prevent oscillation occurring when the negative feed-back is ineffective between sweeps. In a further modification, Fig. 6, during the negative going sweep at point 14, triode 41 is cut off, resistor 10 being returned to an intermediate potential since neon tubes 39, 40 are conducting. At the end of the run-down, valve 7 oscillates producing a negative pulse, which after reflection in line 22, 23 drives valve 7 beyond cut-off, causing biassed diode 49 to conduct and the pulse energy to be absorbed in matching resistor 51. The rise in anode potential causes triode 41 to conduct, thus extinguishing neons 39, 40. Since the grid of valve 7 is effectively connected through resistor 44 to a high negative potential, only the anode potential rises linearly, the grid of triode 41 being held positive due to coupling capacitor 47. When the rate of rise of anode potential of valve 7 is insufficient to maintain grid current in triode 41 it is rapidly cut off, neon tubes 39, 40 restriking to reconnect the grid of valve 7 effectively to a positive potential.